Cathode system for vacuum tubes



Dec. 1, 1931. s. BALLANTINE GATHODE SYSTEM FOR VACUUM TUBES Filed Aug.6, 1928 2 Sheets-Sheet l W 3 7 0 6 Mn L M "A In] Carl/re 75p w a 7M HamiDec. 1, 1931. s. BALLANTINE CATHODE SYSTEM FOR VACUUM TUBES 2Sheets-Sheet 2 Filed Aug. 6, 1928 gwvw tz $41M al/w Patented Dec. 1,1931 PATENT OFFICE STUART BALLANTINE, OF MOUNTAIN LAKES, NEW JERSEYGATHODE SYSTEM FOR VACUUM TUBES Application filed August 6, 1928. SerialNo. 297,746.

This invention relates to vacuum tube devices and to electrical circuitstherefor. More particularly, it relates to that class of vacuum tubedevices in which electron emission is obtained from a cathode systemwhich is heated by alternating current. Such a cathode system may beassociated, in a vacuum tube device, with a suitable anode or plate, asa rectifier, or in conjunction with one or more control elements orgrids, as is common in three electrode and four electrode vacuum tubes,or may be otherwise employed.

"The invention will be described in connection with a vacuum or audiontube of the type. ordinarily used in the telephone and radio arts,although it must be understood that this is only one example of the manyapplioations-of my invention, which extends to X-ray, rectifier, andother kinds of vacuum tubes. l

A method of heating the cathode of an audion or vacuum tube by means ofalternatin current without causing a disturbing electrical pulsation ina circuit associated with the tube has long been sought. In a radioreceiving set, for example, if the filaments of the vacuum tubes aredirectly heated by alternating current it is very diflicult to avoid ahum in the telephones or sound reproducing apparatus. My inventionover.- comes such difliculties, and provides a method and means wherebythe cathode or filament system of a vacuum tube may be supplied withalternating current without the production of undesirable electricalpulsations in the circuits associated therewith.

According to my invention I arrange the cathode system in the form of aplurality of elements having a suitable geometrical arrangement andsupply at least one element with alternating current of a difl'erentphase from that supplied to another element. A0-

cording to a preferred embodiment of my invention, I supply suchelements, in pairs, with alternating currents bearing substantially aquadrature phase relation, so that the current in one element of thecathode system is approximately 90 difierent in phase from the currentin another element of the cathode system. According to my invention,these elements may be arranged either in the same tube, or in separatetubes which are associated externally.

Various arrangements for carrying out my invention are shown in theaccompanying drawings, in which Figure 1 illustrates a vacuum tubeprovided with a two-element cathode; Figure 2 illustrates a suitablemethod of supplying out-of-phase currents to a plurality of cathodeelements; Figure 3 shows another method of accomplishing this result;Figure 4 shows in detail a method of connection to a single tube; andFigure 5 shows an arrangement involving two tubes connected in arallelaccording to the present invention.

simple illustration of the principle of the present invention is givenin Figure 1, which shows a vacuum tube 1 having plate P, grid G, and acathode arranged in the form of two filamentary elements F and F Theseelements may or may not have a common point or centre tap arrangement.If a centre tap is employed, it may be either internalor external, andmay, if desired, make use of a suitable impedance, for example, aresistance, shunted across each cathode element. The elements F and F ofthe cathode system are,in this instance, supplied with alternatingcurrents which bear a substantially quadrature relation to each other;that so is, the current in one element leads the current in the otherelement by approximately 90. If the instantaneous voltage across onecathode element is represented by e =E sin at then the instantaneousvoltage across the second or complementary element may be represented bye =E cos mt, the symbols having their well-known mathematical meanings.

I have found that by this means the hum is greatly reduced orsubstantially eliminated. This result I attribute to the fact that alarge hum-producing component is proportional to the square of thevoltage drop in each element of the cathode. Since sin wt'l' cos wt= 1,it follows that e +c is theoretically constant, and the arrangementproduces an analogous result to that which is obtained when the cathodeis heated by a constant current.

The geometrical configuration of the elemo ments of the filament stemmay be varied considerably, and it is o vious that any number ofelements may be arranged and supplied in the foregoingmanner. Ingeneral, it is useful to arrange the elements in equal or complementarypairs, and a geometrically symmetrical arrangement is suitable.

That portion of the bum which is due to temperature variation of Jouleeffect in the cathode system is not, in general, eliminated by thearrangement described above, and is suitably reduced or overcome byproviding massive cathode elements of high thermal capacity.

Any suitable method of supplying out-ofphase currents to difi'erentelements of the cathode system may be employed. In Figure 2 I haveillustrated one method of accomplishing this result. Two cathodeelements are represented schematically at F and F and may have a centretap or common point if desired.- The two elements are supplied withcurrent from an alternating current source by means of a step-downtransformer having primary winding L and secondary windings L and L bothclosely coupled to the primary and each supplying current to one cathodeelement. A large choke coil L is connected in series with one cathodeelement and its secondary winding, in order to retard that current byapproximately 90". A capacity may, of course, be used instead of a chokecoil, in order to make one current lead by 90. Rheostats R0 may also beemployed in order to control or equalize the currents.

Figure 3 illustrates another suitable arrangement for supplying currentswhich are out of phase. The cathode elements are shown at F and F asbefore and may, for example, be shunted by resistances or otherimpedances Z, providing a centre-tap arrangement. A transformer having acore C is provided with a primary winding L connected to an alternating.current source and a secondary winding L closely coupled to theprimary. The secondary winding L is loosely coupled to the' primary,which may be accomplished by constructing the core with a magnetic shuntS, as shown. The currents supplied by the windings L and L will then beout of phase with each other, and the phase difference may be brought toapproximately 90, or other desired amount, by properly proportioning thetransformer windings and core. Rheostats R0 may be used as before, forequalizing the currents.

Instead of employing a centre tap arrangement in which the grid andplate circuits have a common connection, as illustrated in the foregoingfigures, other arrangements may be employed. For example, the platecircuit may be returned to one terminal of the cathode, as illustratedin Fig. 4. In this case the tube 1 is provided with plate P, grid G, andcathode F, the cathode terminals 3 and 4 being shunted by a suitable imedance Z, for example a resistance. The p ate return through the plateimpedance Z is connected to the cathode terminal 4, and the hum due tothis connection is com ensated by displacing the grid return slig tly toone side of the midpoint of the shunt impedance Z, as by means of thetap5. A practical advantage of this arrangement is that it permits areduced number of leads from the tube.

Figure 5 shows a suitable connection for two tubes arranged in parallel.The principle explained above in connection with Figure 1, in which thecathode elements are lo-. cated in the same tube, applies equally to thearrangement of Figure 5, in which the oathode elements are located inseparate tubes which are externally associated, as by the connectionsshown, or variations thereof, both of these arrangements being includedin the term vacuum tube organization, as employed herein.

Many variations of the specific arrangements shown herein, fall, ofcourse, within the scope ofthe present invention.

I claim:

1. An electrical network comprising a vacuum tube having a cathodesystem comprising a pair of filamentary elements, means for supplyingsaid elements with alternating currents having a substantiallyquadrature relation, and a terminal conductively connected to theelectrical mid-points of each of said elements, said terminal serving asa common terminal for the input and output circuits of said tube.

2. An electrical network comprising a vacuum tube having a cathodesystem comprlslng a pair of filamentary cathodes, sources of alternatingcurrent having a quadrature phase relationship, circuit elements forsupplying the respective filamentary elements with current from saidsources, and leads joining the electrical mid-point of each of saidelements to a terminal, said terminal serving as a common terminal forthe input and output circuits of said tube.

3. In an electrical network, a vacuum tube having input and outputelectrodes and a cathode system, said system comprising two filamentaryelements, means for supplying said elements with alternating currentshaving a quadrature phase relation, a terminal and means establishing atsaid terminal the potentials existing at the electrical midpoints ofeach of said filamentary elements, said terminal serving as a commonterminal for the input and output circuits of said tube.

4. The invention as set forth in claim 3, wherein said means comprisesconnections between said terminal and center taps on said filamentaryelements.

5. The invention as set forth in claim 3, wherein said means comprisesconnections between said terminal and center taps on resistances shuntedacross the respective filamentary elements.

'6. A vacuum tube network comprising, in combination, a cathode systemincluding a plurality of elements, a terminal conductive ly connected tothe electrical mid-points of each of said elements, a source ofalternating current supply, a transformer having a primary windingconnected to said source and a plurality of secondary windings eachconnected to an element of said cathode system to supply currentthereto, and means whereby the currents supplied to said cathodeelements bear a predetermined hase relation.

7 A vacuum tube networ comprising, in

combination, a cathode system including at least two elements, aterminal conductivel connected to the electrical mid-points of eac ofsaid elements, a source of alternating current supply, a transformerhaving a prlma winding and two secondary windings ea connected to anelement of said cathode system to supply current thereto, one of saidsecondary winding? being closely coupled to said primary win 'ng andthe'other of said secondary winding-s being closely coupled to saidprimary win 'ng, whereby the currents supphed to sald cathode elementsbear a predetermined phase relation.

In testimony whereof, I aflix my signature.

STUART BALLANTINE.

